Micrometer head space gauge



Feb. 14, 1950 L. A. WOODWARD MICROMETER HEAD SPACE GAUGE Filed Feb. 20,1948 F/G. i.

w@ mm s 5 7 1 N 3 N0 fr@ a 10 0 5 W M M. A. ZA F 7/w .VY 35 l M ,L 6%

/4 ze z5 Patented Feb. 14, 1950 UNITED STATES PATENT OFFICE 2,497,136MicuoMErnaHEAn SPACE GAUGE LeroyA. Woodward, Dckinson, .'N. Dak.

Application February 20, 1,948, Serial-No. 9,817

(Cl. 33e-.163.)

1 Claim. l My invention relates to gauges for vmeasuring the head spaceof rearms, andmore particularly toA gauges of the micrometer type whichare adapted to be. inserted intothe firing chamber of a firearm tocorrectly and accurately gauge the distance from the forward shoulder ofsuch chamber to the closure for the rear end of the chamber.

In the manufacture ofv rearms, particularly rifles using fixedammunition, it is necessary that the longitudinal dimensions of thefiring chamber be. extremely accurate, whereby the iixed ammunition willhave the snugflt in such chamber with the rear end of the cartridgesnugly abutting the forward face of the closure for the firing chamberwhich usually comprises a bolt. Thus, if the firing chamber is toolongftoo much head space is provided which comprises va space betweenthe rear end of the. cartridgev and the face of the. bolt which makesfor `the creation. oi dangerous pressuresl when the cartridgeis fired.On the contrary, when the ring chamber is. too short, the cartridge willnot extend into it sufriciently, whereby the bolt either will `not closeor will not close completely. Consequently; itis of great interest tothe manufacturer or gunsmith that the longitudinal dimension vof thering chamber be extremely accurately gauged, Whereby the head space isproper for the ammunition for which the gun is designed.

With the. foregoing in view, it is. an object of my invention to.provide an improved head space gauge.

A further object of the invention is to prov-ide an improved head spacegauge in the form of an interior micrometer which is insertable in thefiring chamber ofA a firearm to n ieasure the longitudinal dimensionsthereof.

A further object is to provide in a head space gauge, such as that lastdescribed, means for locking the beam and the sleeve of the gaugetogether in a pre-set relation to each other.

Other objects and advantages reside in the particular construction ofthe device according to the invention, combination and arrangement ofthe several parts thereof, and will. be readily understood by thoseskilled in the art upon reference to the attached drawing in connectionwith the following specification, wherein the invention is shown,described and claimed.

In the drawing:

Figure 1 is an elevation of a preferred form of the invention;

Figure 2 is a view like Figure 1, but showing a portion of the outersleeve in longitudinal vertical section;

'Figure als. an end view looking from the right of Figure l;

.Figure 4 is a transverse vertical section taken substantially on theplane of the line 4-4 of Figure 2;:

Figure: 5 is an end. elevation of a locking device looking from .theleft of Figure 6;

.Figure 6 is a longitudinal vertical. sectionV through the lockingvdevicev of Figure 5;

Figure 7 is a longitudinal vertical section through `the. butt end of arearm showing the gauge according to the; invention in use.

Referringspeciflcally to the drawing, wherein like referencev charactershave been used throughout. the several views to designate like parts,and referring more specifically to Figure '7, Ill desigf nates generallythe rear end of a barrel for anrearm which. includes the usual bore IIwhich merges with shoulders I2 into a ring chamber I3 at the rear end.The iiring chamber |31 is normally closed at the rear by a movableclosure I4, such as a bolt. Any suitable cartridge, not showmhaving ashell case complementary to the shape of `the firing chamber I3 isadapted to be positioned in the ring chamber I3 and. secured therein bya bolt I4 for firing.

The gauge according to the invention comprises a sleeve generallyindicated by I5 which comprises` a reduced central section I5 andenlarged end sections. .I8 land I9. The diametric dimensions of theAenlarged sections I3 and I9 are such as to be substantiallycomplementary to the in, terior of the firing chamber I 3. The frontsection I8- merges into an inwardly-directed substam tiallynostro-.conical shoulder vIl which is com! plementaryto the shoulder I2of the firing cham ber. The reduced central section Iii may be providedw-ith knurling 2B to provide a grip thereon. Obviously, the reducedcentral section I6 is not adapted to come. in contact with the walls ofthe .firing chamber I3, whereby to permit the knul-ling` or stamping ofmarkings on the centr-afl section I8, The rear enlarged section I9 maybe inscribed with a suitable zero marker 2I.

The sleeve I5 is formed with an interior 'bore Z2 which extendsrearwardly from the forward end thereof. The bore 22 is unthreaded andthe forward end is outwardly flared to provide a substantiallyfrustro-conical recess 23 which faces forwardly of the front end of thesleeve, Rearwardly, the bore 22 merges into an enlarged and threadedcounter-bore 24 which in turn, in the region of the enlarged rearsection IB, merges 3 into a still further enlarged and unthreadedcounter-bore 25.

A beam 26 is concentrically disposed within the sleeve I 5. The beamcomprises a graduated rear end section 2T which is formed with asuitable zero graduation 2t and plus and minus grad uations 2S and 38,Figure 2. The rear end of the section 2l extends outwardly of the secondcounter-bore 25 and is formed to provide the measuring head 3l. Theforward portion of the section 21 is slidable into and out of thecounterbore 25 in axial directions. A measuring thread section 32 of thebeam 2% extends forwardly of the graduated section 2l and is threadedlyreceived in the interioriy-threaded-counter-bore 24 of the sleeve. Acylindrical forward extension 33 of the beam is slidably received in thebore v22 of the sleeve and includes a terminal portion 34, a, part ofwhich at least extends outwardly or forwardly of the forward end of thesleeve l5. A lock' nut 3S is threaded on the threaded terminal portion3d of the beam and comprises an interiorly threaded sleeve member havinga substantially frusto-conical rear end 36 which is formed with aplurality of radially-directed slots 31. The frusto-conical rear end 36is adapted to be substantially complementary to the frustoconical recess23 in the forti ard end of the sleeve l5. The outer periphery of the nut35 may be knurled or otherwise formed to provide a gripping surface.Such surface is best indicated at 38, in Figure 1.

In operation, the gauge according to the invention is inserted into aiiring chamber i3 of a firearm, Figure 7, with the zero indicia orcalibrations 2l and 28 of the sleeve and beam aligned. The bolt orclosure it for the firing chamber is now closed. Assuming that thefiring chamber i 3 involved is too short, the bolt will either refuse toclose entirely or will close only with a substantially great effort.This indicates that the firing chamber is too short, as the gauge whenset with the zero indicia aligned is of the correct length to correspondto the cartridge designed for use in the particular gun. It should bementioned at this time that prior to inserting the gauge into the firingchamber initially, the sleeve and beam are locked in the Zerindicatingposition by 'means of the lock nut 35 which is screwed down so that thespring end formed by the slots 3l is forced into locking and wedgingengagement with the recess 23 oi' the sleeve and the threads of thethreaded portion 34 of the beam. Upon the determination that the firingchamber I3 is too short, as aforesaid, the gauge is removed from thefiring chamber, and the beam 25 is screwed ina' direction to shorten thelength of the same and register one of the minus graduations 29' of thebeam with the Zero indicator 2l of the sleeve. The lock nut 335 is oncemore tightened to lock the parts together and the gauge is reinserted inthe ring chamber and the bolt is again closed. Assuming that the boltnow works freely, the setting of the gauge is noted, the lock nut isloosened, and the gauge is reset at an intermediate point between. thelast reading and the Zero settings. Once more the gauge is inserted intothe ring chamber, and the bolt closed. Assume ing now that the boltagain works 'too tightly, the setting is once more noted and the newsetting of the gauge is made until the proper and accurate measurementof the longitudinal dimensions of the firing chamber is accomplished.The gauge will then indicate in the example described the amount bywhich the firing chamber I3 must be enlarged by boring away of theshoulder I 2 thereof to insure proper head space between the rear of thecartridge and the forward face o the bolt i4. Obviously, when theinitial test o the firing chamber indicates that the same is too long,the procedure is reversed until there as been determined the amount bywhich the firing chamber must be shortened by sawing off the rear end ofthe barrel I0.

By providing means for locking the moving parts of the gauge togetherduring a, measuring operation, extremely great accuracy is obtained andthere is no danger of inaccurate readings caused by relative rotation ofthe parts during the opening and closing of the bolt and/or in theinsertion or removal of the gauge from the chamber. Wear of the gaugeparts is readily compensated for by setting the same to a position whereit correctly designates the correct size of a desired iiring chamber andthen remarking the sleeve part i9 with a new zero setting 2| inalignment with the zero calibration 28 of the beam.

Thus, while I have shown and described what is now thought to be apreferred embodiment of the invention, it is to be understood that thesame is susceptible of other forms and expressions. Consequently, I donot limit myself to the precise structure shown and describedhereinabove except as hereinafter claimed.

I claim: l

In a head space micrometer for measuring the distance from theinternally shouldered forward end of a ring chamber to the forward endof a closed breech closure, including an internally threaded sleevesubstantially complementary to said chamber and having front and rearends, a beam having external threads at an intermediate portion thereof,said beam being threaded in said sleeve and having front and rear endsextending axially outwardly of both ends thereof, and a head formed onsaid rear end of said beam for engagement with said closure, theimprovement comprising other screw threads formed on said front end ofsaid beam, a lock nut threadedly and adjustbly engaged with said lastnamed threads, said sleeve including a. forward end formed with aforwardly-directed frusto-conical recess axially thereof, said lock nutincluding a rear end formed with a rearwardly-directed frusto-conicalsleeve engaging end, and said sleeve engaging end of said nut beingwedgingly seatable in said recess, whereby to lock said beam and sleevein pre-set relation to each other.

. LEROY A. WOODWARD.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 729,970 V4Spalding June 2, 19031,351,721 Eickhoff et al.\ Aug. 31, 1920 2,340,428 Ramsdell Feb. 1, 1944

